Dunno if anyone here has dealt with this problem, but for what it's worth:

I acquired a used tank with a few pieces of equipment including a hood, but the light fixture has been removed from the hood. I don't mean just the bulb. I mean in the place where the fixture ought to be, there is just a pair of wires dangling in the middle, no socket to put a bulb into.

How much of a hassle would it be to replace the fixture? Can I take the hood to Home Depot or Radio Shack and have someone there fix it for me, or at least tell me how to fix it? Or am I better off just buying a new hood for $40? I have already purchased a new Eclipse Mini filter, otherwise I'd be inclined to get an Eclipse hood.

If the hood is 24 inches here's what you'll want to do. Ahsupply has complete retrofit kits that will fit in there (probably the seller took it back out when he sold it.)

If you don't go with a retrofit kit, take the bulb, or bulb size for the hood, add an inch for the end caps and go shopping. If you only have a Home depot, buy two lamp holders or end caps for a normal output fluor. tube. Next by an electronic ballast for the diameter and wattage of the bulb you bought. The 1inch skinnies are called T8 for example.
Compact flour. bulbs are often T5s.
Once you buy the electronic ballast (don't buy the heavy magnetic!) its a simple as following the wiring diagram on top of the ballast to wire lamp to ballast and ground it.

Or you can simply go buy a new light fixture from the LFS and donate the empty light housing to a keener like me!

Good luck_________________Discus Man is gone... I remain... #6... I am not a number I am a free man!